class_docstr: Container for cluster load metrics.
  
  Metrics here are updated from raylet heartbeats. The autoscaler
  queries these metrics to determine when to scale up, and which nodes
  can be removed.
code: def is_active(self, ip):
      return ip in self.last_heartbeat_time_by_ip
  
imports: import logging
  import time
  from collections import Counter
  from functools import reduce
  from typing import Dict, List
  from ray._private.gcs_utils import PlacementGroupTableData
  from ray.autoscaler._private.constants import AUTOSCALER_MAX_RESOURCE_DEMAND_VECTOR_SIZE, AUTOSCALER_REPORT_PER_NODE_STATUS
  from ray.autoscaler._private.util import DictCount, LoadMetricsSummary, NodeIP, ResourceDict
  from ray.core.generated.common_pb2 import PlacementStrategy
label_desc: Use image node_id 5 for calling the LoadMetrics obj's underlying member method code with example usage: obj.is_active(ip) and returns: unknown